Pallet lift truck



Dec. 20, 1955 D. GOLD PALLET LIFT TRUCK Filed Nov. 3, 1953 United States Patent O PALLET LIFT TRUCK David Gold, Pittsburgh, Pa. Application November 3, 1953, serial No. 390,613

6 Claims. (ci. 28o- 44) This invention relates `to hand lift trucks of the type used for lifting and transporting material handling pallets, and, more particularly, is directed to improvements for facilitating movement of the truck frameto an operative lifting position relative to a pallet.

The frames of pallet handling lift trucks have a fork shape providing a pair of spaced forwardly extending arms which are inserted in the space between the upper and lower platforms of material handling pallets preparatory to lifting the same. The frame is supported for rolling movement over a floor area by wheels at the rear thereof and by wheels or rollers at the forward ends of the fork arms which are extensibly mounted with respect to the frame by supporting brackets pivoted to the frame. After movement of the fork arms to an operative position between the upper and lower pallet platforms, pivotal movement of the supporting brackets raises the fork arms of` the truck frame into engagement with the underside ofthe upper pallet platform and elevates the pallet so that it may be transported by the truck.

Since the fork arms of the truck must be inserted in the relatively narrow space between the upper and lower lower pallet platforms is increased when the platforms are constructed of spaced parallel Wood slats since the extensible rollers, without more, drop into the space between adjacent slats whenever they move over one of the slats so that each of the slats becomes an obstruction over which the extensible roller must move.

To facilitate entry of the truck fork arms into the space between the pallet platforms, various proposals have been made for elevating the forward ends of such arms and the extensibly mounted rollers carried thereby with respect to obstructions an amount such that the rollers will more readily move over such obstructions. One proposal for this purpose comprises a series of auxiliary rollers mounted at different levels in advance of the extensible truck rollers.

Another proposal for the same purpose comprises a camming member in advance of the extensible rollers. Undesirable features are presented by both of these proposals since the first elfects elevation of the truck frame over obstructions with a series of bumping movements and the second, while eliminating the bumping movement of the first, results in a frictional drag of its cammingmember over the obstruction which impedes forward movement of ice the truck. These features of the patented proposals are eliminated by the elevating provisions of this invention.

One of the principal objects of this invention is to provide an auxiliary mechanism which will elevate the extensible rollers of hand lift trucks over obstructions, such as a lower pallet platform in the path of movement of the truck, without any noticeable bumping movement or frictional drag. To this end, there is provided on the forward endof each truck frame fork arm an elongated roller which extends angularly with respect to the horizontal centerline of the fork arm on which it is mounted and which has a line of contact on its lower surface sloping downwardly from front to rear with respect to such forkarm. In a manner to be described, the elongated rollers may be eitherV conical or cylindrical and are preferably mounted so that their angularly inclined axes converge toward the front of the truck.

Other objects and advantages of the invention will become apparent from the following description.

In the drawings, there are shown two embodiments of the invention. In this showing:

Fig. l is a bottom plan view of a pallet lift truck illustrating the arrangement of auxiliary elevating rollers at the forward ends of the truck lift arms in accordance with the principles of this invention, the actuating mechanism for operating the extensible elevating rollers being broken away;

Fig. 2 is a side elevational view of the truck shown in Fig. 1;Y

Fig. 3 is a fragmentary view similar to a portion of Fig. 1 showing a modified arrangement of auxiliary lifting rolling; and

Fig. 4 is a side elevational view of the apparatus shown in Fig. 3.

In the drawings, the numeral 1 designates as a whole a pallet lift truck comprising a frame 2 of fork shape having a pair of forwardly projecting lift arms 3 which are connected together at the rear ends thereof by a transversely extending supporting member 4. The transverse supporting member 4 is secured to a housing 5 which is supported at its lower end by a pair of floor engaging Wheels 6. The housing 5 includes mechanisms (not shown) for elevating the housing 5 and frame 2 with respect to the Wheels 6 and foractuating the supporting rollers at the front of the fork arms 3 to an extended position ina manner to be described.

The supporting rollers at the front ends of the fork lift arms 3 are designated by the numeral 7. Each of the rollers 7 is rotatably connected to the outer end of a bracket 8 which has its inner end pivotally connected to the frame by a pivot 9 extending transversely of one of the fork arms 3. The 'bracket support S includes an eccentrically projecting bracket part 10 to which an actuating rod 11 is connected,`

The drawings show the position of the supporting brackets 8 and rollers 7 in their unextended or withdrawn position in which the frame 3 is supported at its minimum position above the floor level. When the rods 11 are pulled rearwardly by the actuating mechanism (not shown) in the housing 5, theV eccentric bracket part 10 and the bracket support 8 are rotated in a clockwise direction as viewed in Fig. 2 to move the supporting rollers 7 downwardly with respect to the frame 2 and thereby elevate the fork arms 3 with respect lto the floor level on which the truck is supported and lift a pallet which may have its upper supporting platform positioned above the fork arms 3. f

The pallet lift truck structure thus far described is conventional and forms nopart per se of this-invention.

As indicated above, the fork arms 3 are moved to an operative lifting position with respect to a pallet by wheeling the truck over the oor area on which the pallet is supported to insert the fork arms 3 in the space between the upper and lower platforms of the pallet. The lower platform pallet of course constitutes an' obstruction to the forward movement of the extensible roller 7 through the space between it and the upper pallet platform. 'Since the space between the upper and lower pallet platforms is relatively small. in depth, the supporting rollerA 7 must have a relatively small diameter of the natureillustrated n the drawings. By reason of the small diameter of the rollers 7, the lower pallet platform constitutes anlobstruction in the path of rolling movement of the roller 7 which renders the operation of inserting the fork arms 3.in ,the space between the upper and lower pallet platforms .ditlicult. The difficulty of this operation is of course increased when the pallet is constructed of spaced parallel Wooden slats.

In accordance with the principles of this invention and for the purpose of elevating the forward ends of the fork arms 3 over an obstruction such as a lower pallet platform in the path of movement of the rollers 7, each forward end of the fork arms 3 is provided with an elongated roller 12 in advance of the rollers 7 which is journaled in front and rear brackets 13 and 13a depending from the under surface of the fork arms 3 at the forward ends thereof. As best shown in Fig. 1, the axes of the rollersw12 extend angularly and transversely with respect to the horizontal centerline of the arms 3, and, preferably, the axes of the rollers 12 converge toward the front of the truck. .In the showing of Figs. 1 and 2, the rollers 12,are cylindrical, and the rear brackets 13a are positioned at a lower level than the front brackets 13. In this manner, asbest shown in Fig. 2, each roller 12 has a line of contact. 14 along its lower edge which slopes upwardly toward the front of the truck. The line of contact at the point 15 at the front of the roller 12 is preferably positioned at a level which is slightly above the upper surface of` a lower platform pallet, and its rear point 16 is positioned just slightly above the lower level of the roller 7. The point 16 is positioned sufficiently close to the point 17 of rolling contact of the roller 7 such that the roller 7 will be in engagement with a lower slat of a slatted pallet before the point 16 moves out of engagement with such slat. In other` words, the minimum `linear distance between the points 16 and 17 is determined by the width of one of theslats in a slatted pallet. The linear distance between the points 16 and 15 in a direction extending longitudinally of the fork arms 3 must also be somewhat greater lthan the `spacing between adjacent slatsof the lslatted pallet to be handled so that the point 15 will be positioned overa succeeding slat when the point 16 rnoves beyond-thepreceding pallet slat. Therollersllhavea length suchfthat the distance between the points 15 andpvl in a direction transverse of the fork arms 3 approximates the length of the rollers 7.

In the modification shownuin Figs. 3 and 4,; a-modiied roller 12a of conical shape is employed in place-` of the cylindrical roller 12 of Figs. 1 and,2. The axesof the rollers 12a are positionedin ahorizontalrplane,mandthe journalsupports 18 provided byithe VVbrackets, 19V are positioned at the same verticallevel, thelsloping line of contact l14 of the rollers 12a.being provided bythe LCQIlial shape thereof and being otherwise the same asv described in connection with theshowings of Fig. 2. Inthe'fpmodilication shown in Figs. 3 and 4, there is .further illustrated a modified, form of supporting rollers 7a. and ;piyoted molllltingbracket ,Stag this further modicationhavingv-no ,bearing onthe present invention.

The operation of Atherollers,12 and. 12z will-be` best understood by; considering :their .actioas :the fgrkfarms are moved into the space between the upper anddower platforms of a pallet to be lifted and transported by the -truck. As initial entry of the forward ends of the. arms 3 into this space is elfected, the line of contact 14 will strike the upper surface of the lower platform at a point slightly inwardly of the point 15. As further forward movement is continued, the line of contact 14 of the rollers 12 or 12a will lift the forward end of the arms 3 upwardly with a combined rolling and sliding action over the upper surface of the lower pallet platform. This elevating movement raises the supporting rollers 7 so that the point 17 is positioned at substantially the same level as the upper surface of the pallet platform when it moves into supporting engagement therewith. `In this manner, the supporting rollers 7 move into supporting engagement with the upper surface of the lower pallet platform smoothly and without any noticeable jarringaction against the rollers 7 or thev actuating mechanism including the bracket 8 by which they are moved to an extended position. l l

Auxiliary rollers 20 are mounted on the brackets 8 and a level slightly above the level of the rollers 7 to protect the rollers 7 during rearward movement in accordance with conventional practice.

,While I have illustrated and described several specific embodiments of my invention, it will be understood that this is merely by way of illustration, and thatvarious changes and ,modifications may be made therein within the contemplation of the invention and under the s cope of the following claims.

l claim:

l. `ln a pallet lift truck having a pair of spaced forwardly projecting fork arms and a pair of supporting rollers respectively mounted Aadjacent the forward ends of said arms for vertical movement from a retracted to an` extended position, an auxiliary mechanism for lifting said'arrns vand rollers over obstructionsI in the path of rolling movement/of said rollers comprising an elongated roll ymounted `of each arm and positioned in advance -of said supporting roller, each of said elongated rolls havingian axis of rotation inclined angularly with respect to thelongitudinal ,center line of said arrns andhavingvan obstruction engaging line of rolling and sliding contact at its periphery which slopes in an upward direction toward the outer end of said arms. l

`2..l`hev invention described in `claim l characterized byqsaid lines of rolling and sliding contact of each said rolls havinga length `in a direction` transversely of .the truck forkuarrns suchuthat its ends are in positions of alignment with the ends ofthev supporting roller on the forkarm mounting the elongated roller providing said line of rollingand sliding contact.

3. The invention described in claim l characterized by `saidelongated rolls being cylindrical in `shape and respectivelyhavingsupporting brackets at their lends povsitionedat different vertical levels, v the bracket at the front end being at `a level above that of the bracket at the rear endwof the roll. I l

4. Flfheinvention described in claim l ycharacterized by said elongatedwrolls respectively having a frustoconical shape and having journal supports at the same ,vertical` levels on said arm, the .smaller ends offsaid elongated rolls being positioned forwardly of their larger ends relative Itothe arms on which theyv are mounted.

5. The invention described in claim l characterized by the angularlyinclined axes yof said elongated rolls converging toward theforward yendsof said arms.

6. ln a pallet lift ytruck having a frame in the shape of a fork providing laterally spaced `forwardly projecting lift arms, supporting wheels at the rear of said frame, and apair of supporting rollers respectively mounted at the forward ends ofdifferent ones of said arms for vertical movement from a retractedto an extended position, the invention which ycomprises an auxiliary mechanism for Alifting said arms, and rollers o ver an obstruction in thevpathof l,rolling.movement of said ,rollers comprising laigv'pairdof Ielongated rolls Vrespectively lmounted on said arms in positions in advance of said supporting rollers, each of said elongated rolls having an axis inclined angularly with respect to the longitudinal center line of said arms and having a line of rolling and sliding contact at its bottom which slopes in an upward direction toward the outer end of said arms, the ends of said line of contact at the rear of said elongated rolls being positioned slightly above the line of rolling Contact of said supporting rollers with a oor area when in their retracted position and the opposite ends of said line of Contact being at a sufficiently higher level to clear the upper surface of an obstruction over which said supporting rollers are to be moved.

References Cited in the le of this patent UNITED STATES PATENTS 2,498,504 Quayle Feb. 21, 1950 2,635,926 Michalowski Apr. 21, 1953 FOREIGN PATENTS 835,699 Germany Apr. 3, 1952 

